Repeated, within-session resurgence.

Resurgence is a reliable, transient effect that only occasionally is replicated more than once within a single experiment or subject. In the present experiments, within-session resurgence was generated repeatedly by dividing individual sessions into three phases (Training, Alternative-Reinforcement, and Resurgence-Test). In Experiments 1 and 2, resurgence reliably occurred in most of the 22-30 daily sessions when responding was reinforced on, respectively, fixed- and variable-interval schedules. Resurgence magnitude and duration did decrease across replications for some subjects, but not for others. To examine the utility of the procedure in studying the effects of an independent variable on resurgence, in Experiment 3 the effects of rich and lean baseline and alternative reinforcement rates on resurgence were compared. The target response was eliminated more rapidly, resurgence occurred more often, and usually was greater following rich alternative reinforcement rates. Resurgence was of greater magnitude when the baseline reinforcement rate was relatively lean compared to the alternative reinforcement rate. These experiments provide a reliable method for generating resurgence within individual sessions, instead of across multiple-session conditions, that can be repeated over many successive sessions.

Baseline response rates affect resistance to change.

The effect of response rates on resistance to change, measured as resistance to extinction, was examined in two experiments. In Experiment 1, responding in transition from a variable-ratio schedule and its yoked-interval counterpart to extinction was compared with pigeons. Following training on a multiple variable-ratio yoked-interval schedule of reinforcement, in which response rates were higher in the former component, reinforcement was removed from both components during a single extended extinction session. Resistance to extinction in the yoked-interval component was always either greater or equal to that in the variable-ratio component. In Experiment 2, resistance to extinction was compared for two groups of rats that exhibited either high or low response rates when maintained on identical variable-interval schedules. Resistance to extinction was greater for the lower-response-rate group. These results suggest that baseline response rate can contribute to resistance to change. Such effects, however, can only be revealed when baseline response rate and reinforcement rate are disentangled (Experiments 1 and 2) from the more usual circumstance where the two covary. Furthermore, they are more cleanly revealed when the programmed contingencies controlling high and low response rates are identical, as in Experiment 2.

On defining resurgence.

A review of different investigators' definitions of resurgence revealed several common features: First, characteristics of the resurgent, or target, response, such as its transience; magnitude; time course within and across sessions; and relativity to a baseline response rate are not mentioned. Second, the target response is described as being established through its reinforcement in the first, or Training, phase of a resurgence procedure. Third, the target response must be eliminated as an alternative response is reinforced in the second, Alternative Reinforcement, phase of a resurgence procedure. Fourth, the alternative response must be extinguished during the Resurgence Test phase. Fifth, none of the definitions allude to any contribution of stimulus variables to resurgence. When reconsidered in light of contemporary research germane to these features, none of the reviewed definitions sufficiently reflect important variables in the generation and assessment of resurgence. The review concludes with a proposed working definition that takes into account contemporary research involving all of the aforementioned factors.

Combinations of response-reinforcer relations in periodic and aperiodic schedules.

Key pecking of 4 pigeons was studied under a two-component multiple schedule in which food deliveries were arranged according to a fixed and a variable interfood interval. The percentage of response-dependent food in each component was varied, first in ascending (0, 10, 30, 70 and 100%) and then in descending orders, in successive conditions. The change in response rates was positively related to the percentage of response-dependent food in each schedule component. Across conditions, positively accelerated and linear patterns of responding occurred consistently in the fixed and variable components, respectively. These results suggest that the response-food dependency determines response rates in periodic and aperiodic schedules, and that the temporal distribution of food determines response patterns independently of the response-food dependency. Running rates, but not postfood pauses, also were positively related to the percentage of dependent food in each condition, in both fixed and variable components. Thus, the relation between overall response rate and the percentage of dependent food was mediated by responding that occurred after postfood pausing. The findings together extend previous studies wherein the dependency was either always present or absent, and increase the generality of the effects of variations in the response-food dependency from aperiodic to periodic schedules.

Enhanced U.S. Army HIV diagnostic algorithm used to diagnose acute HIV infection in a deployed soldier.

Antibody screening alone may fail to detect human immunodeficiency virus (HIV) in recently infected individuals. By U.S. Army regulation, HIV-infected soldiers are not permitted to deploy to areas of conflict, including Iraq and Afghanistan. We report here the first case of acute HIV infection (AHI) in a soldier in a combat area of operation detected by an enhanced U.S. Army HIV testing algorithm and discuss features of the tests which aided in clinical diagnosis. We tested the sample from the AHI case with a third generation HIV-1/HIV-2 plus O enzyme immunoassay, HIV-1 Western Blot, and a qualitative HIV-1 ribonucleic acid molecular diagnostic assay. Risk factors for HIV acquisition were elicited in an epidemiologic interview. Evaluation of the blood sample for AHI indicated an inconclusive serologic profile and a reactive HIV-1 ribonucleic acid result. The main risk factor for acquisition reported was unprotected sexual intercourse with casual strangers in the U.S. while on leave during deployment. The clinical diagnosis of AHI in a combat area of operation is important. Diagnosis of HIV is key to preventing adverse effects to the infected soldier from deployment stressors of deployment and further transmission via parenteral or sexual exposures.